The present invention relates to a carrier used to support and protect semiconductor wafers during various manufacturing processes related to wafer polishing. More particularly, the present invention teaches an improvement in the carrier, including an increase in the number of support ribs and a lighter weight, to ensure high-quality results and facilitate automated or manual loading/unloading operations of the carrier.
The semiconductor industry produces vast quantities of semiconductor wafers; i.e., thin slices of a semiconductive material used as a base for an electronic component or integrated circuit. Wafers comprise, for example, such materials as gallium arsenide, lithium niobate, sapphire, quartz and may be used in industries other than the semiconductor industry. Each wafer typically includes a flat, highly polished surface critical to formation of the integrated circuit and performance of the semiconductor. Wafers are polished to improve their surface quality, improve the uniformity of the wafer thickness, and ensure the integrity of the wafer. The geometry and quality of the surface, therefore, are an absolute prerequisite to product performance in this field of endeavor.
The industry currently relies on polishing machines to polish semiconductor wafers (hereafter, wafers). Typically, each machine is equipped with multiple heads mounted on the machine and each head is holding a carrier. The bottom part of the carrier resembles a flat disk. A template is affixed to it, usually by pressure sensitive adhesive (PSA). Templates are used to facilitate mounting of the wafers on the carriers.
During the process, a vertical force exerted on the heads of the machine brings the wafer into contact with a polishing pad of the machine. To polish the wafers, a surface of each wafer is brought into contact with the polishing pad. The heads rotate to provide a cycloidal movement to the wafers, and the polishing pad is subjected to a rotational force, such interaction between the wafer surface and the polishing pad causing the surface of each wafer to be polished.
Many polishing machines and carriers are built according to the design described in U.S. Pat. No. 4,194,324. The carriers of these machines and templates share general characteristics such as a relatively thin template having an outside diameter approximately equal to the diameter of the associated carrier. Most templates have round recesses, which accommodate approximately two thirds of a wafer, leaving a surface of the wafer exposed. The bottom of the recess of the template is designed to hold the wafer through water surface tension, adhesion or other means. Generally, the thickness of the material between the wafer and the carrier is uniform.
Issues abound with the current art, however. The load from the head to the carrier cannot be transferred uniformly due to the inventory of interacting components; e.g., head, o-ring, and carrier. A toroidal torsional load acts on the cross-section of the carrier as a result of the concentrated force from the head and distributed load from the wafers. Each of the aforementioned conditions produces aberrant finals results in the polished surface and the uniformity of the wafer. Such abnormalities preclude satisfactory construction conditions for the integrated circuit on the polished surface of the wafer. Additionally, the wafer carrier reception of load from the bottom of the head is concentrated only where carriers contain wafers and not to carriers empty thereof. This also results in a lack of uniformity of load and additional complexities in the carrier load condition. During the polishing operation, wear and friction heat is generated on the polished surface of the wafer. This heat transfers up through the thickness of the carrier and creates the undesirable effect of changing the shape of the carrier. Finally, and most importantly, the relatively heavy weight and cumbersome nature of the carriers unnecessarily encumbers the human operators charged with loading and unloading carriers to and from polishing machines.
What is needed, therefore, is a wafer carrier having acceptable structural and performance qualities that overcome the issues of the current art.
The present invention provides an improved carrier for disc-shaped objects such as semiconductor wafers, and a method for carrying such an object. The carrier boasts exceptional structural design and performance characteristics, including a particularly lightweight, highly maneuverable carrier that accepts and facilitates external forces to optimize results of polishing procedures. Additionally, the carrier of the present invention houses and protects the wafers to prevent degradation of quality, form, or value of the wafer relative to optimal polishing performance within predetermined tolerance specifications.
In one embodiment, the present invention includes a flexible plate; an annular vertical wall and a plurality of ribs. The plate provides a generally disk-shaped, relatively thin, flexible base for the carrier. An annular wall extends upward from the plate, the annular wall having an annular flange located on an upper part of the wall opposite the plate. The annular flange includes an annular protrusion and receives a load for polishing; a wafer. The ribs radially extend from the wall in a direction toward the perimeter of the plate and in a direction toward the center of the plate.
Further advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.